Purifying phthalic anhydride



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' ,LLOYD'QIDANIELS, GFQRAETON,PENNSYLVANIA,' ASSIGNOR; BYntnsimhsslentmme T0 THESELDEN RESEARCH & ENGINEERINQCORPRATION,forPItrmsBUBGHsPErmv fsYL AmA, A cortrom'rrclvior'. DELAWARET; 1a e g l min I PuRIrYINe hmrrmnid v 1 'ADPl ication seems at 7 1Thisinventicn relates te purificatinn (if;

.{ihthalic anhydride; and more particularly'ftq itspurifi cat-ien bydistillation; precesses.

phthalicanhydridevapors,aflar ge propertion v 7 infi'which case'the'values are Obtained, as

v b 'lnthe ,conimercial manufacture of phthalic anhyd ide bythecatalytic Oxidation of naphthalene and fractional condensation of the Qct thefc'ondensat'e contains impurities suehfas, j alphanaphthaqumone; rmalelcj ac1 d,' benzo c acid and tarrybcdiee jvhiehjeause discolc'ragtiQn Qfj the' product-;;and lower its market value." "Su h impurelpredat e m n y purified by; prolonged" heating, 'eitheryvit h or Withoutcondensing agents, followe'd by' dis 5 tillation Of'th product fro theundesired.

impuritieswhich i have been; rendered less volatile "by the treatment"The. impurities themselves are thusleftbehind in the lstillfas Of adarkcclc'red tarorgcoke; I

The ccndensatien Ofthe impurities by this methcdis quite complete and itis :p ssibIe'tO' a residue vWhich eventually; takes lthe'f heat thestill residues tqquite high tempera;

tures and t o.distillflpractically all ofthe phthalic anhydride fr m theresidue yvithcut: Carrying ever-much of theaii'r'lpurities,Zand

. vforthisfreasonthe practicehasbeen tc'distill the greatest possible.aincunt of phthalic' an;

still to gh temperatures; nd results not only in Warpingandthusfshorteningthellife' Whenithad accumulatedinvsuflicientquanti hasbeen allowed tc' accuznulate; thefstill be 7 Y ofthe stilli but'producesa hard layer of coke fever the bottom cf'the still which is :a poorconductor of heatand requires even more in tense heat after a feacharges have been run.

; Fer this reason the practice has been toguse' pot stills withsuccessiyecherges whichfhave' beensrun' by the batch processanid thecoke in g cooled and the hard; cokeremcvedby hand ties 7 a c Inf spite'of the short lifei and "frequent shutdcwns of the pot stills, this methcdhasbeen previously Considered the 'most economical because itreccvers-almostall of the phth'alic' anhydride from the condensedimpurities and thusmroduces a higher yield fof available ,prodifct.f'The coke itselfhas been'ccnsidered lesefiserm N65 458317. 7 p 7,practically worthless and; l1a s'f:u'sual;ly bee discarded asawasteproductL 1 "Thi present invjentlon is based enfthe suriprisingfdisccv ery that the phthalic anhy A dri l'e contained inthestilliresi duecanbe i'ecovered i'n excellent purity means lof leach-iving; The leaching may be effected bji w'ater;

phthalie acid3 or it'may bee tfectedby alkaline sclutions suehas dilute,ainmeni'umflhydrox idegin which case'a salt Of thelphthalidacid isobtaineclfAs the phthalic.'anhydride inz the stillf re siclu"canflrea'dily' be recovered by tire process: H

According to the'present invention'the distillation of" theimpurephthalic anhydride:

'isfcarriedrout fromlalrgestillsbyeither the continucusor batch"pr0cess,j local (werheat ing being prevented by ccntinuous agitatorsand-- the temperature Oflthe residue being" inain-tz 'iined below35,0 lnthisway the residue in the stilljisf always liquid and it is entirelyfeasible to 'usefretary agitators, the

s shoes of which would have 'been clcgged or broken the hard coke'forlnedat the higher 80' we I tenine'ratures previ0usly used; The tarryresidue is allowedjto'l'emain in'thestilladdi tional inclten phthalicanhydride being a'ddedthereto, until a -suflicient charge-hasaccumulated to befdra' wn off. into'inculdsa-in which it" is-all'ow'edtoccoland harden; The

presence of a 'liquidlin'ithe still bottom at all times prevents unevenheating and Warping ofthie still-and theinuch lower temperatures 3 usedresultin; a greatly increased life forthe entire apparatus.

in the still afterthe phthalicanhydride has been-distilledfrcm it is afactor in the sur The Prolonged lg'f the t'arry' residue.

results in; further condensation .of the -ini-' purities found in theoriginal charge and als b 1n pyrogenet e condensation ofma of them forexample; the maleic acid'which may be the distillation process but toobtain an ac-- tual increase in the total amount of phthalicrecovered'as anhydride and acid.

To prepare the still residue for leaching, a

number of processes may be used. The soft tar may be hardened in mouldsand then ground, or it may be flaked on a rotary drum, or porousmaterial such as cinders, coke and the like may be incorporated with itwhile it is still soft and the-hard product broken into pieces. Moreoverthe residue, While yet in the still, may be subjected to physical orchemical treatment to aid in the leaching. For example, it is known thatthe acid salts of phthalic acid, and particularly the acid salts of thealkali metal, are more soluble than is phthalic acid itself; therefore,the residue .which may contain up to 50% of phthalic acid may bepartially neutralized to form these acid salts, which are more readilyleached. o

i The leaching itself may take place by any of the usual processes, butsince it is desirable to" recover the phthalic acid in as strong a.solution as possible the percolation or open drainage method ispreferred. A particular ly eflective method of procedure, for use whenthe residue has been ground is to moistenthe mass thoroughlywith water,thus agglomerating the fines onto the coarse particles and then tosubmit the mass to continuous recirculation of a small stream of theleaching liquid from above,the residue itself being retained on a screenor other foraminated foundation to permit ready drainage of the liquidwhich is recirculated to dissolve further values.v As above stated, theleach-v ing liquid may be water or a dilute solution of an alkali suchas ammonia, but it is to be noted that in cases where alkaline solutionsare used the solution must not be too concentrated nor may more thanenough alkali be present than the amount required for completeneutralization of the phthalieacid or certain colored impurities will bedissolved from the residue along with the phthalic anhydride values. a qa p It is to be noted that the product obtained by drawing off theresidue as a liquid is itself a valuable product aside from the value ofits phthalic anhydride content. It is a synthetic resin containing alarge proportion of phthalic anhydride in extremely uniformdistribution, and subsequent grinding and treatment with glycerol orother polybasic alcohols will produce a commercial resin having manydesirable properties. I I

The invention will be described in greater detail in connection with thefollowing exer ones.

amples, it being understood that these are entirely for purposes ofillustration and that the invention is not limited thereto.

E trample 1 other impurities is charged in successive batches into amelter from which it is run into a horizontal still of 18,000 poundsworking capacity.- The molten material is continuously agitated anddistilled until the boiling pointiof the residue is about 1025 C. abovethat of phthalic anhydride, at which point, a'new charge is introduced.The distillation is repeated, allowing the residue to remain in thestill under continuous heating and agitation until a sufiicient amounthas accumulated after which it is drawn off as a dark limpid liquid andallowed to harden in moulds.

The hardened product, which contains 20-50% of phthalic anhydride and nomaleic anhydride, is then ground and leached with water, the recovery of'phthalic acid amounting to 90-l00%- of theory expressed as phthalicanhydride.

Emample 2 thoroughly moistened with water in order to agglomerate thefiner particles onto the coars- It is then placed in anopen drainagetank and leached with a ti-10% ammonia solution, the leaching liquidbeing continuously drawn off at the bottom of the tank and returned tothe top. Practically all of the remaining phthalic anhydride visrecovered as ammonium phthalate containing more or less acidammoniumphthalate.

Example 3 i A phthalic anhvdride product is distilled as described inExamples 1 and 2 but the residue,.instead of being run into moulds, 1s

flaked bvhardeningon a water-cooled drum followed bv scraping with aknife. The product, which is quite brittle, is obtained in the formofthin flakes which are easily ground. After grinding the product ischargedinto two or more leaching vats and leached bythe open drainagemethod on the countercurrent principle. The leaching liquid used in thelast vat, which consists of a dilute solution of ammonium orsodium'hydroxlde, contains insufiicient alkali to form V the normal-phth'alate,so,thattheacid salt is I tralized withmore of sodium orammonium acid obtained. The drainage from this vat is neusodium orammonium hydr'oxide to form the normal salt after, which it is passedthrough the next precedingvat" whereit is again transformed into theacid In thismanner concentrated solutions phthalate may be'obtained'without .the danger of excess alkali which would causethe'solution of un-, desired impurities; The partly; exhausted salt,

. residue i'n-the latervats of the seriesis con:

i cessive increments of impure phthalic anhydride tinuously leached withmore dilute solution,

thus obtainin an acid phthalate solution which is suit'ale forsubsequent leaching of! additional fresh material 'in "earlier Ivats' rin the series. 1 .Whatisclaimed asn'ewisr 1., .Aprocess which comprisesdlstilling impure phthalic anhydride below the temperature of hard coke.formation and running off the stillresidue as. liquid. V

2.. process which comprises charging sue-- low the temperature'o'f hardcoke-formation untila sufiicient 3. process which comprises subjectingto continued heat mg, distillingoffithejmajor portion of, the

Y phthalic anhyd'ride therefrom below the tem= perature of hard. cokeformation, the residue to further continued 4 low the ltemperatureofhard coke formation the, distillation of subjecting heating beandrunning it-ofi', as a liquid.

1 ing impure 4. A process which comprises-subjecting impure phthalic"anhydride. to 7 continued opA process which ,comprisessubjectheating inthe molten state of condensation 7 agents, major portion of thetherefrom below, the temperature of hard- ,in the presence cokeformations'and running the residueofffi as-a liquid. I a

6. .A process which comprises subjecting impure phthalic anhydride tocontinued heatng in the molten state in the presence of condensationagents, distilling ofi' the major por- 7 tion of the phthalicanhydridetherefrom below the temperature of hard coke formation, subjectingtinued heating, during'subsequent addition and distillation offurtherincrements of residue as impure phthalic. anhydride'intoa still,distilling ofi the major portion of the phthalic anhydride therefrombeamountofresidue has 1 ace r cumulated, and running on? this residue asa I liquid.

.maj or portion of phthaliclanhydride to continued 1 distilling off theI phthalic' anhydride the ,lfesidu furtherConpurephthanc'anfiyuridsbdowth -t mpera ture of hardcore formationgandrunn'ingfit 'off as a liquidr- 751 processaccording r-toiclaim 1, inwhich the .;-impure phthalifcuanhydride'. is' obtained tram-the tualene"I l H c, v 8; A; process according-to claim13, in which the impurephthalic anhydride is obtainedfrom the catal ic air oxidation fof; mph.

i-eees-saeeording toclaini-5,in which mre phthalic 'a'nhydridei'sobtained catalytic 1- -air oxidationF of naplr- I '80 process "which'compi'ises idistilling impure plithalic-anhydride below -tl1eitmpeifature. of hard coke fforma tion, running ofi' -the a liquid,allowing the residue ,to

harden; and leaching thel'ha'rdened residue fwitha solution. which does{not 'fconta'in "fa greater amountejf alkalithanthat mo11cu1ar--lyequivalent to the 'ent in th'eresidu'e; V

llbA process of 'puri fiyin phthalic ianhydride below-the temperatufieoffilhard coke formation which comprisesfdistillingiit, sub Y jectingthe residue to continued the temperature of hard coke formatiomdischarging. the residue as a: liquid, hardening heating below and breakingup the. residue, andrecovering i phthalic anhydride values therefrom byleachingwith a solution which'does not con tain a greater amount fofalkali! than that r molecularly equivalent to the lphthalic .an-

hydride present in the residue. I v- 12 A process of treating stillresidue from pure phthalic anhydride below the temperature of hardcoke-formation whichcomprises discharging it fromthe stillas a liquid,allowing the liquid to harden,

and grindingthe hardened residue.

anhydride'v'alues from residue fromgthe distillation of impure 'phthalicanhydride which" comprisesleaching it. with a solution which does notcontain greater amount of alkali than that phthalic anhydride present inthe residue. 14'. The process of recovering phthalic an hydridejvaluesfromiresi'due from the distil- 13. The process 'of' recoveringv-phthalicmolecularly equivalent to thefl 'lation of impure phthalicanhydridewhich comprises leaching it with aleachingagent selected fromthegroup'consisting of water,

aqueous alkaline solutions, and solutions of soluble salts of phthalicacid with asolutiona which does not contain agreater amount, of j alkalithanthat molecularly equivalentto the T I phthalicaanhydride present inthe residue. 15. The process of recovering phthalic anhydride values'fromfresidue from thedistillation' of impure phthalic anhydride I whichI comprises leaching it with an aqueous solu-' tion of ammoniumphthalate;

16,; The process of'recovering phthalic an- I 'g- 29th day of May,

I not being sufiicientlyin molecularly corresponding to the phthalic I Ikali present after hydridevalues from residue from the distillation of,impure phthalio anhydride which comprises leaching it with a solution ofammon um hydroxide, the amount of ammonia excess of the amount anhydridepresent in the residue to substantiall dissolve impurities soluble inammonium ydroxide solutions;

17. A process of recovering phthalic anhydride values from hardenedstill residue from the vdistillation of impure phthalicvanhydride whichcomprises leaching it with an alkaline solution, the amount anhydride,present in the residue being insufficient to dissolve impurities solublein solutions containing free alkali. v

, 18. Still residue from the heating and distillation of impurecatalytic phthalic anhydride below the temperature of hard cokeformation which has been run from the still .in liquid form and allowedto harden.

Pittsburgh, Pennsylvania, this Signed at 1930. l -LLOYD C. DANIELS.

of free 211- reaction with the phthalic I

